Acoustic emission has been observed in the α ⇋ β transition of monocrystalline samples of paradichlorobenzene. No acoustic emission has been detected in the β → α transition of single crystals nor in the α ⇋ β transitions in polycrystalline samples. The simultaneous observation of acoustic emission and Nuclear Quadrupole Resonance when several α ⇋ β transition cycles are carried out reveals some features of this solid state phase transition.